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CARTO, Utility or Futility. Introduction :. The localization and navigation of EP catheters by fluoroscopy may have he following problems: the inability to accurately associate intracardiac electrograms with their precise location
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Introduction: • The localization and navigation of EP catheters by fluoroscopy may have he following problems: • the inability to accurately associate intracardiac electrograms with their precise location • (2) the endocardial surface is invisible using fluoroscopy and the target sites can only be approximated by their relationship with nearby structures • ( 3) navigation is not exact, time consuming, and requires multiple views to estimate the three-D location of the catheter • (4) inability to accurately return the catheter precisely to a previously mapped site; • (5) exposure of the patient and medical team to radiation.
Newer mapping systems have revolutionized the EP lab. aimed at • improving the resolution, • three-dimensional spatial localization, • rapidity of acquisition of cardiac activation maps. However, these mapping systems are very expensive and not required for the commoner clinical arrhythmias like AVNRT, accessory pathway mediated tachycardia (WPW syndrome and concealed pathways) and typical atrial flutter.
Non-contact Endocardial mapping Endocardial Solutions (ESI) system: • Myocardial potentials are reconstructed from data acquired by recording cavity potential from an array of electrodes sitting in the blood pool within the cardiac chamber and not in endocardial contact. • Inverse- solution methods are applied to these non-contact signals in order to reconstruct endocardial potentials from the raw cavity potentials.
Endocardial Solutions mapping showing the earliest activation (in red color) in a case of focal atrial tachycardia. The upper right hand panel displays AP projection on the left and LAO projection on the right side. The lower half of the picture shows intracardiac tracings.
The Endocardial Solutions electrode array mounted on a 9F catheter.
The main advantage of this system is that it requires only one beat to reconstruct a complete activation map, which potentially allows mapping of hemodynamically unstable arrhythmias. • However, the distance between the endocardial wall and the balloon center and the spatial complexity of the activation patterns influences the accuracy of the electrogram reconstruction negatively. • This will affect the reliability when mapping for example, dilated LVs or complex reentrant circuits.
Validation in treatment of atrial tachyarrhythmias • The system has been found to facilitate ablation of atrial tachycardia, both focal and reentrant. • It has proven useful in patients with multiple foci and in those with atypical macro-reentrant circuits due to unique anatomy and/or the result of corrective surgery • In patients with recurrent atrial flutter despite attempted cavo-tricuspid isthmus block, it helped to determine the “gap” in the line of block • The system has also been useful in setting of focal atrial fibrillation ablation by localizing left atrial ectopic activity and identifying the arrhythmogenic pulmonary vein
Contact Mapping system • Electroanatomical mapping (CARTO System) The technology is based on a catheter location system, which determines a mapping catheter's position and attitude within an ultra low magnetic field emitted from radiators positioned under the operating table.
System Components: • The catheter resembles a standard 7- or 8- Fr deflectable catheter with a 4-mm tip and proximal 2-mm ring electrodes. • The location sensors lie just proximal to the tip electrode, totally embedded within the catheter. The three location sensors are located orthogonally to each other. • The locator pad is placed beneath the operating table and includes three coils that generate ultralow magnetic fields, which decay as a function of the distance from their sources. • The resolution of the location capabilities of the system has been previously been shown to be <1 mm in both in vitro and in vivo studies.
A tiny location sensor is embedded in the catheter tip consisting of three miniaturized coils that is tracked by the CARTO system. The locator pad placed beneath the patient table generates 3 ultra-low magnetic fields to identify the location and orientation of the sensor Typical setup of the CARTO electroanatomical mapping system in the EP lab.
This system enables • tracking of the tip of the mapping catheter within the heart • navigation of the catheter independent of fluoroscopy. • Signals received within the sensor are transmitted along the catheter shaft to the main processing unit.
Mapping procedure: • The reference catheter is placed inside the CA or the RV. • The mapping/ ablation catheter is introduced and placed in the chamber being mapping. • The mapping system determines the location and orientation of both the mapping and reference catheters. • The location of the mapping catheter is gated to a fiducial point in the cardiac cycle and recorded relative to the location of the fixed reference catheter at that time, thus compensated for both subject and cardiac motion. • By moving the catheter inside the heart, the system continuously analyzes its location and presents it to the user, thus enabling navigation without the use of fluoroscopy.
Mapping procedure: (cont.) (6)The mapping catheter is dragged over the endocardium, sequentially acquiring the location of its tip together with the local electrogram when the catheter is in stable contact with the wall. (7) By sampling the location of the catheter together with the local electrogram from a plurality of endocardial sites, the three-dimensional anatomy of the chamber is reconstructed in real-time. (8) The local activation time is then color-coded and superimposed on the anatomical map with red indicating early-activated sites, blue and purple late activated areas, and yellow and green areas intermediate activation times
Mapping procedure: (cont.) The stability of the catheter and contact is evaluated at every site by examining the following criteria: (1) local activation time stability, which is defined as the difference in ms between the local activation calculated from two consecutive beats; (2) location stability, defined as the distance in mm between two consecutive gated locations; (3) Morphological superpositioning of the intracardaic electrogram recorded on two consecutive beats; (4) Cycle length stability, defined as the difference between the cycle length of the last beat and the median cycle length during the procedure.
Mapping procedure: (cont.) • The three-dimensional geometry of the chamber is generated using a modified "star“ reconstruction algorithm. • The sets of points from endocardial surface are used for geometrical reconstruction. • It is recommended to map each chamber in a different reconstruction bin ('chamber setup"), when mapping more than one chamber, which can be simultaneously displayed.
Mapping procedure: (cont.) The electroanatomical maps can be presented in either two or three dimensions as activation, isochronal, propagation, or voltage maps. • The activation maps display the local activation time color-coded overlaid on the reconstructed three-dimensional geometry • The propagation map shows a dynamic color display of the propagation of the activation wavefront across the reconstructed chamber. • The voltage map displays the peak-to-peak amplitude of the electrogram sampled at each site. This value is color-coded, with red and purple indicating areas with the lowest and highest amplitude The abnormal low voltage usually represents scar tissue and thus may help in understanding the mechanism underlying the arrhythmia.
Advantages • The ability to accurately relocate and thus revisit areas of interest within the heart offers a significant advantage in successful ablation of arrhythmias. • It is capable of creating a voltage map of the chamber of interest that is useful in determining location of surgical or post-infarction scars and determining their participation in reentrant arrhythmias. • The ability to register the location of individual RF lesions, which facilitates the creation of complex lesion sets (linear lesions).
Important cardiac structures as His bundle, ostia of venous structures, valve annuli and scar tissue can be tagged properly, which are avoided during ablation. • The ability to tag previously unsuccessful ablation sites also helps to identify the correct location for ablation, which may be useful in difficult cases of arrhythmia such as atrial tachycardia or VT of focal origin or of right free wall AP
Clinical Applications of Electroanatomical Mapping in atrial tachyarrhythmias The capabilities of the CARTO system to associate relevant electrophysiological information with the appropriate spatial location in the heart and to accurately determine the three-D location and orientation of the ablation catheter The technology enables • To define the mechanism underlying the arrhythmia, • To design the ablation strategy, • Finally to return accurately to the desired site for the delivery of RF energy.
Atrial Tachycardias: • The CARTO facilitates catheter ablation of ectopic atrial tachycardia by providing a precise anatomic reconstruction of the atria. • In most cases with sustained or frequently recurrent atrial tachycardias, successful results are obtained usually with a small number of radiofrequency applications at the earliest endocardial activation site • Intraatrial macroreentrant tachycardias frequently complicate the clinical course in patients with congenital heart disease who have undergone palliative surgical interventions. Multiple isolated channels between scars and anatomical barriers are responsible for these macroreentries. • Ablative therapy with radiofrequency energy offers a potential for cure for those patients. Three-dimensional mapping allows visualization of the activation wavefronts along anatomical and surgically created barriers and has shown promising results in guiding ablative therapy
Electroanatomic mapping on CARTO system of focal right atrial tachycardia showing earliest activation (red color) below crista terminalis. LAO 40° projection (Figure 3A) and RAO 30° projection (Figure 3B).
(A) CARTO magnetic electroanatomic map of the RA during atrial tachycardia in a rotated left lateral projection. This is an activation map and the adjacent bar shows the color code–red being earliest and purple the last to get activated. The red dot on the map encircled by black interrupted lines is the site of earliest activation; surface ECG of the atrial tachycardia is shown in (B).
Atrial flutter: • CARTO mapping can be expected to provide only minor benefit in typical atrial flutter as the success rate in isthmus dependent atrial flutter has approached 90 to 95% • The system allows precise localization of the anatomical boundaries of the reentrant circuit and facilitates ablation by guiding linear lesion creation and may help to reduce the fluoroscopy exposure. • It provides unique views that cannot be obtained by conventional fluoroscopy, such as the bottom view, which fully exposes the flutter isthmus and facilitates rapid ablation procedures by using minimal approaches. • The CARTO system may also be particularly useful in identifying the gaps in the ablation line using activation or propagation maps in the setting of recurrent flutter after previous ablation, to guide repeat ablation. • In patients with atypical left atrial flutters, the reentry circuit with a protected isthmus can be identified in most patients by electroanatomic mapping.
Atrial Fibrillation: • Electroanatomic mapping can guide percutaneous linear lesion creation mimicking the surgical maze procedure. However, this can be a time consuming process and completeness of linear lesions is difficult to assure. • Linear lesions performed in the left atrium using percutaneous catheter approaches or by surgical means are often proarrhythmic leading to incisional flutters. Electroanatomic mapping may be useful in identification of the remaining gaps and ablation of residual flutters. • Circumferential radiofrequency ablation of pulmonary vein ostia under electroanatomic mapping guidance has been introduced as an anatomic approach for curing atrial fibrillation.
CARTO map of the left atrium during sinus rhythm in a patient undergoing focal atrial fibrillation ablation. The map is in a right lateral projection and shows the position of the three pulmonary veins. Radiofrequency lesions (red dots) are delivered at the ostium of the RSPV for isolation.
Limitations: The system is limited to point-to-point mapping strategy. Thus, if the arrhythmias are non-sustained or quickly change to a different morphology or mechanism, e.g., atrial tachycardia degenerates to atrial fibrillation, mapping of such arrhythmias will be difficult to complete and the procedure is likely to take considerable time.
2) Basket Catheter mapping: • Simultaneous mapping of multiple points performed using 64 -pole endocardial basket catheter. • Current designs of basket arrays consist of a series of equally spaced electrode pairs mounted on eight flexible splines, and each spline contains eight electrodes which can be straightened and advance into the cardiac chamber, so that the splines deploy and are apposed against the endocardium • The basket catheter was connected via the amplifier to the three-D mapping system, which provides three-D color construction of electrical activity.
Basket mapping of normal sinus rhythm. The right upper panel shows the potential map, the earliest activation (red color) at the site of sinus node. In addition, the splines of basket catheters are aligned with the endocardial wall. The right lower panel shows isochronal map of the sinus rhythm. The left panel shows the electrogram from the different splines.
It Shows different splines of basket catheter in the right atrium. The isochronal and potential maps are suggestive of ectopic atrial beat.
Advantages of Basket Catheter: • It provides simultaneous, multiple, stable recordings for most of the endocardial surface. • The color-coded animation images help in establishing the relationship between activation patterns and anatomic structures. • It allows high density mapping from infrequent ectopic beats. • By mapping the precise location, the number of RF ablations may be reduced substantially.
Limitations: • Basket catheters do not at all points orient themselves towards the endocardium in the shape expected of them and this may vitiate our judgment. • Basket catheters have large area near the shaft without electrodes, therefore during mapping some part of endocardium is not in contact with the basket. • There is a potential risk of thrombo-embolism with left sided mapping.
3) Real-time positional management (Cardiac Pathways) EP system: Reference and ablation catheters: • Two reference catheters and one mapping/ablation catheter are introduced One reference catheter is positioned in the CS, and the other in the RV apex. For ablation purpose 4-mm tip bidirectional steerable cooled ablation catheter is used . • The reference catheters are equipped with four-ultrasound transducers and the ablation catheter contains three ultrasound transducers. • The ultrasound transmitter device sends a continuous cycle of ultrasound pulses to the transducers of the reference and ablation catheters. • By measuring the time delay from the departure of a transmitted ultrasound pulse and the reception of this pulse at the other transducers, the distance between the individual transducers can be calculated to locate the catheter(s) within the reference frame. Once the 3D-reference frame is established, triangulation can be used to track the position of additional transducers.
Isochronal mapping on Real Position Management System, showing the reference catheter position in coronary sinus and right atrium; and, ablation / mapping catheter in leftatrium (AP projection).
Real-time position management (RPM) mapping system: • The 3D real-time position management and mapping system uses ultrasound-ranging techniques to determine the position of a mapping/ ablation catheter relative to two reference catheters. • The mapping system consists of an acquisition module and an ultrasound transmitter and receiver unit, both connected to a SPARC 20 computer. • Electrograms and catheter positions are stored on optical disk. The original position of the reference catheters can be displayed on the real- time window, thereby allowing repositioning of catheters after displacement
Use of this system may result in reduced fluoroscopy time. • Routine application of the real-time position management system requires only the use of special catheters; no additional catheters or skin electrodes are needed. • As any type of catheter containing ultrasound transducers can be "tracked" within the reference frame and used to locate positions.This may be useful in case of the creation of linear lesions in atrial fibrillation patients. • The ability to create lesions within a defined area will allow systematic ablation of endocardial zones of slow conduction critical for the perpetuation of reentrant VT. The limitation of this system • occasional failure of ultrasound transducers, requiring replacement of a catheter. • Secondly, a "Voltage map" cannot be obtained unlike the other systems described
Isochronal map of right atrium on Cardiac Pathways System showing the earliest activation site (red color) at the junction of right atrium and superior vena cava (AP Projection)The right panel of the picture shows earliest activation signal in the ablation catheter (56 ms early from the reference catheter).
Conclusion • The newer mapping system reduces fluoroscopic time for ablation without compromising efficacy or safety. • These newer mapping systems are useful tool for guiding catheter ablation of unstable arrhythmias (e.g., ventricular tachycardia) and complex atrial arrhythmias. • The newer mapping systems at present are not cost-effective for developing countries. • Since the special catheters used for nonfluoroscopic mapping are relatively expensive than the conventional catheters, they should not be used with arrhythmias that are relatively simple and easy to ablate, such as AVNRT, preexcitation syndrome, or AV nodal junctional ablation.
